Explosion zones: what they mean and who decides them
Your works changed and the classification on the wall did not, so that zone is no longer a label — it is a historical statement you are still buying against. Get it right and the equipment question answers itself in one line of a table.
The decision in front of you
A zone is a statement about air, not about hardware
Directive 1999/92/EC sorts places where an explosive atmosphere may occur into six zones: three for gases, vapours and mists, three for combustible dust. The criterion is always a probability, never a quantity — how often and how long the atmosphere is actually there.
"In normal operation" is the phrase that carries the whole classification. It includes start-up, shutdown, sampling, filling and routine maintenance. It does not include a burst hose or a failed gasket, because those are faults — which is why a place that only becomes hazardous when something breaks is usually zone 2 or 22.
Everything that follows — which category of equipment may be installed, what has to be inspected and how often — comes out of that one judgement.
- Zone 0 and 20: present continuously, for long periods or frequently
- Zone 1 and 21: likely to occur occasionally in normal operation
- Zone 2 and 22: not likely in normal operation, and brief if it occurs
How it is derived
Five steps, and none of them can be skipped
Each step depends on the answer to the one before it, which is why a zone cannot be read off a list of plant types.
Establish the substances and their properties
Flash point, explosion limits, ignition temperature and vapour density for liquids and gases; for dusts the particle size distribution, minimum ignition energy and the behaviour of a deposited layer. Safety data sheets are the starting point, not the conclusion — a solvent whose flash point drops in service behaves differently from the data sheet.
Identify and grade every release source
A release source is a specific point, not a room: a flange, a shaft seal, a filling connection, a sampling valve, an open manway. Each is graded as continuous, primary or secondary depending on whether it releases permanently, during normal operation, or only in the event of a fault.
Assess ventilation and containment
The same release in a well-ventilated outdoor structure and in a closed room produces very different zones. Availability of the ventilation counts too: an extraction system that can fail without being noticed cannot be credited in full.
Derive the zone type and its extent
Now the zone follows from the grade of the release source and the degree of ventilation. The extent is part of the result — a zone has a shape, and equipment at its boundary is either inside or outside, never approximately.
Record it, and keep it current
Zone plan, protective measures, coordination with other employers on site, and the inspection regime go into the explosion protection document. A new substance, an additional filling point or a modified extraction system reopens the assessment; the document is a live record, not a one-off exercise.
Beyond the table
Three things a zone table never shows you
Dust is not gas with bigger molecules. A dust zone is defined by the cloud, but a settled layer is a hazard of its own: a single pressure wave lifts it, and it insulates hot surfaces so that a motor which stays inside its temperature class in clean air no longer does under 5 mm of deposit.
The extent of a zone is not a radius you can look up. It follows from release rate, substance, geometry and ventilation — which is why most retrofit problems appear here: a new pump or a relocated vent changes the shape, and a junction box that used to sit outside now sits inside.
And zones expire in practice rather than on paper. If the works has changed and the document has not, the classification on the wall is a historical statement.
- Cleaning intervals belong in the protection concept, not in the housekeeping schedule
- Equipment and protective systems every three years, the installation as a whole every six
- Ventilation and gas detection annually — BetrSichV Annex 2, section 3, nos. 5.1 to 5.3
The one-directional rule
Which equipment category each zone requires
From Annex II, part A, no. 2.3 of Directive 1999/92/EC. A higher category is always allowed, a lower one never.
| Zone | Explosive atmosphere is … | Minimum equipment category | Equipment protection level |
|---|---|---|---|
| 0 (gas, vapour, mist) | present continuously, for long periods or frequently | 1G | Ga |
| 1 (gas) | likely to occur occasionally in normal operation | 2G | Gb |
| 2 (gas) | not likely in normal operation, and brief if it occurs | 3G | Gc |
| 20 (dust) | present as a cloud continuously, for long periods or frequently | 1D | Da |
| 21 (dust) | likely to occur occasionally in normal operation | 2D | Db |
| 22 (dust) | not likely in normal operation, and brief if it occurs | 3D | Dc |
Next
From the zone to the equipment
- ATEX basics and markingThe equipment side: categories, certificates and the spare parts that void an approval.
- Pressure Equipment DirectiveThe other directive that decides whether a component may carry CE at all.
- Measurement and test equipmentStandard versions with the range and the material at the position.
- Electrical componentsFor everything outside a classified area.
Two ways in
Start from the document, order from the table
shukchok is an open marketplace for industrial goods: outside a classified area you can compare and buy today, with the specification above the price and no login in between. Inside one, the range grows through suppliers who carry Ex versions and their certificates — listing them here costs no fee at all.